Long responses are fully scrollable without overflow clipping

Fixed-height message bubbles silently amputate long AI responses, hiding answers that the user paid tokens to generate. Users have no indication that content is missing, which creates a trust problem: they believe the AI gave a short or incomplete answer when in fact the UI is simply clipping it. This is especially damaging for technical content like long code blocks, step-by-step instructions, or multi-paragraph analysis where the hidden portion often contains the conclusion or the critical step.

Remove fixed height constraints from individual message bubble components in src/components/chat/MessageBubble.tsx. Let each bubble expand naturally with its content and place the scroll container at the message list level, not on individual messages.

.message-list { overflow-y: auto; height: 100%; }
.message-bubble { padding: 1rem; border-radius: 0.5rem; }